Electrical switching devices, such as circuit breakers, have the task of decoupling one or a number of consumers from a power supply network if a specific fault occurs. The classical fault is the occurrence of a short-circuit current, and the circuit breakers are usually configured to move a switching unit during such a short-circuit current and thus to decouple the connection between consumers and the power supply network.
After an electrical switching device of this type has tripped, the switching unit of the electrical switching device is reset. This means that the switching unit is moved from a TRIP position into a RESET position by means of a swivel lever. This reset process forms part of a switching process of an electrical switching device and it is therefore necessary, after tripping the switching device, to reset the switching device by way of a reset process in order then to be able switch on the same.
During the reset process, in other words the movement of the swivel lever of the switching device from the TRIP position into the RESET position, the spring element or elements, which press or presses the pawl of the switching unit of the electrical switching device against a tensioning lever of the switching unit, are tensioned. This is necessary since large forces are required in order to close the contacts of the electrical switching device when switching on the electrical switching device.
One of the main problems during the reset process is the friction of components in the switching unit, in particular between the surfaces of the tripping mechanism, in particular the tripping shaft, and the pawl, which are in contact with one another during the reset process, in other words the movement of the switching unit from the TRIP position into the RESET position. If the friction between the pawl and the tripping mechanism is too great for instance, it may ensue that the pawl cannot slide from the contact surface of the tripping mechanism and can therefore not pivot. In this case, the pawl cannot be moved or reset and the electrical switching device, for instance a compact circuit breaker, cannot be switched on after the reset process. If the pawl cannot be released from the contact surface of the tripping mechanism, in particular the tripping shaft, the switching unit is not correctly reset, so that during the subsequent switch-on of the electrical switching device or switching unit of the electrical switching device, the pawl cannot hold the tensioning lever of the switching unit in the RESET position and the switching unit is therefore not transferred into the ON position, but instead into the TRIP position.
With the Modeion-3VT1 circuit breaker by Siemens AG, the problem was hitherto solved as follows: FIG. 1 shows a schematic representation of a part of the switching unit of this known circuit breaker. In this FIG. 1, the circuit breaker is tripped, in other words it is in the TRIP position. An operator of the circuit breaker can reset the switching unit of the circuit breaker by actuating the tensioning lever 5.
The switching unit comprises a pawl 2 and a tripping mechanism 1. The pawl 2 and the tripping mechanism 1 are mounted in a pivotable and rotatable manner on a side wall 10 of the circuit breaker. A pawl spring 9 is clamped between the pawl 2 and the tripping mechanism 1, which exerts a required torque on the pawl 2 and also on the tripping mechanism 1. The force exerted by the pawl spring 9 or the torque exerted by the pawl spring 9 generates contact forces and frictional forces between the tripping mechanism 1 and the pawl 2.
During the reset process, it should be ensured that the frictional forces between the pawl 2 and the tripping mechanism 1 do not prevent the pawl 2 from pivoting or rotating in the direction toward the tensioning lever 5 of the switching unit. The pawl 2 must pivot or rotate in order to jump onto the tensioning lever 5. If the operator relinquishes control of the tensioning lever 5 in the RESET position, spring elements, in particular also the pawl spring 9, of the switching unit, generate a torque which pivots the tensioning lever 5, so that the tensioning lever 5, in particular the contact surface 7 of the tensioning lever 5, comes into contact with the pawl 2, in other words the contact surface 8 of the pawl 2.
Subsequently the pawl 2 pivots and is stopped in the RESET position by the contact surface 6 of the tripping mechanism 1. After the RESET position of the switching unit is reached, the circuit breaker can be switched on. In order to implement the switch-on process, the frictional torque between the pawl 2, in other words the contact surface 8 of the pawl 2, and the tripping mechanism 1, in other words the contact surface 7 of the tripping mechanism 1, must be smaller than the torque available to rotate the pawl 2 in the direction of the tensioning lever 2. This is ensured in the Modeion-3VT1 circuit breaker by different timing sequences of different parts of the pawl 2 and of the tripping mechanism 1.
The pawl 2 has a curved region 11 with a chamfer 12. The tripping mechanism 1 accordingly comprises an additional hook 3. These two elements or surfaces 12, 3 are in contact during the reset process in order mainly to reduce the frictional forces and also to protect sensitive surfaces of the tripping mechanism 1 and the pawl 2, in particular the contact surface 4 of the pawl 2, which is in contact with the tensioning lever 5 when the circuit breaker is switched on and which has to fulfill its function if the circuit breaker is tripped.
An additional hook 3 or an additional surface is provided for the movement of the tripping mechanism 1, which is/are in contact with the pawl 2 and therefore rotates the same. This prevents the contact surface 12 of the pawl 2 from coming into contact with a corner of the tripping mechanism 1. Accordingly, there is no friction between these two parts, which means that lower forces are needed to move the tripping mechanism 1.
The Modeion-3VT1 circuit breaker is disadvantageous in that additional elements, such as the hook 3 of the tripping mechanism 1 and the curved region 11 of the pawl 2 are needed in order to ensure the functionality of the switching unit. These additional elements are especially cost-intensive. More material is required on the one hand and on the other hand these elements must be manufactured very precisely and calibrated to one another in order to ensure the functionality of the switching unit and thus of the circuit breaker, in particular of the reset process of the switching unit of the circuit breaker.